Slavery eventually would have died out, my guess is by the early 20th century.
Our military wouldn't have developed the weaponry we did, which would have left us behind the eightball for the Spanish American War and possibly WWI.
Lincoln probably would have been a one term president.
Grant, Garfield, Hayes and McKinley may not have been elected.
These are of course in my humble opinion only, and given more time I could think of other significant differences. But this may be food for fodder.